JP2011526956A - Moisture crosslinkable polyethylene composition - Google Patents

Abstract

  The present invention is a moisture crosslinkable composition. This may be (i) a blend of a nonpolar polyolefin and a second highly polar or amorphous polyolefin, or (ii) a copolymer of a nonpolar polyolefin and a second polar or amorphous polyolefin. it can. The present invention is useful for the preparation of moisture-cured wires, cables, films, pipes, hot melt adhesives, and other extruded or injection molded articles. The present invention is also useful for the preparation of media that rapidly transport selected species, including film membranes.

Description

  The present invention relates to a moisture crosslinkable composition. More particularly, the present invention relates to moisture crosslinkable blends of non-polar polyolefins and highly polar or amorphous polyolefins.

  Moist crosslinking using a direct process (grafting the silane and simultaneously making the article), a silane pre-grafted resin, or a reactor copolymer requires the use of a high temperature curing medium such as steam or sauna. Furthermore, the direct moisture cross-linking process is controlled centralized. Technical know-how is needed to handle silane and peroxide, to accurately measure, and to ensure the quality of the finished product.

  In a moisture cross-linking process using a silane pre-grafted resin, the grafting step is performed in a reactive extrusion line and is costly. Furthermore, silane pre-grafted resins have a limited shelf life compared to reactor copolymer products.

  Under ambient conditions, the cure rate of the polyethylene composition is slow (1 to 2 weeks), limiting productivity. If an expensive catalyst with a fast cure rate is used in the curing technique under ambient conditions, the crosslinkable polyethylene composition undergoes premature crosslinking. In order to prevent premature crosslinking, scorch control additives are used, further increasing the overall cost of the system.

  (A) Does not require a reactive extrusion step, (b) produces a smooth and uniform article, (c) does not require intensive control, and (d) allows fast curing in hot water or under ambient conditions What is needed is a crosslinkable polyethylene composition.

  The present invention achieves these objects and the like. The present invention includes a first polyolefin and a second polyolefin. The second polyolefin is selected from polar polyolefins, amorphous polyolefins, and mixtures thereof. The second polymer can be finely dispersed or copolymerized with the first polymer.

  Without being bound to a particular theory, the present invention takes advantage of the solubility characteristics of polar or highly amorphous phases that absorb high levels of silane / peroxide and allow for rapid incorporation in the polyolefin phase. It is thought that.

  When the polar polyolefin or the highly amorphous polyolefin is finely dispersed in the base polyolefin according to the present invention, (a) the immersion time of the crosslinking agent is shortened by 10 times compared to the base resin, and (b) by extrusion of the composition Cross-linking occurs at a rate that is smoother than that achieved with (c) grafted or reactor silane copolymers. Furthermore, it is pointed out that the composition of the present invention crosslinks faster than normal systems using moisture cross-linking catalysts such as sulfonic acids using standard levels of dibutyltin dilaurate (DBTDL) catalyst under ambient conditions. Is done.

  According to the present invention, (1) the use of a shorter extrusion line, (2) a longer production time, and (3) an economical hindered phenolic antioxidant that currently cannot be used with sulfonic acids. It can be used.

  The present invention is useful for the preparation of moisture-cured wires, cables, films, pipes, hot melt adhesives, and other extruded or injection molded articles. The present invention is also useful for the preparation of media that rapidly transport selected species, including film membranes.

It is a graph which shows the influence which the addition to the nonpolar polyolefin of polar polyolefin has on the relationship between the immersion time and the wetness obtained after addition of vinyl alkoxysilane and an organic peroxide. Graph showing the effect of addition of polar polyolefins to non-polar polyolefins on the relationship between cure time and high temperature creep elongation (at ambient conditions), including a comparison of moisture crosslinkable compositions containing sulfonic acid catalysts It is.

  The crosslinkable composition of the present invention includes (1) a first polyolefin, (2) a second polyolefin, (3) a vinylalkoxysilane, and (4) an organic peroxide. The second polyolefin is selected from polar polyolefins, amorphous polyolefins, and mixtures thereof. The second polymer can be finely dispersed or copolymerized with the first polymer.

  Suitable first polyolefins include polyethylene and polypropylene. A polyethylene polymer, as the term is used herein, is a homopolymer of ethylene or ethylene with a small proportion of 3 to 12 carbon atoms, preferably 4 to 8 carbon atoms. Copolymers of one or more α-olefins and optionally dienes, or mixtures or blends of such homopolymers and copolymers. The mixture can be a mechanical blend or an in situ blend. Examples of α-olefins are propylene, 1-butene, 1-hexene, 4-methyl-1-pentene, and 1-octene.

  The polyethylene can be homogeneous or heterogeneous. Homogeneous polyethylene has a polydispersity (Mw / Mn) usually in the range of 1.5 to 3.5 and an essentially uniform comonomer distribution, which is relatively low as measured by differential scanning calorimetry. Characterized by a single melting point. Heterogeneous polyethylene usually has a polydispersity (Mw / Mn) higher than 3.5 and no uniform comonomer distribution. Mw is defined as the weight average molecular weight, and Mn is defined as the number average molecular weight.

  The polyethylene can have a density in the range of 0.860 to 0.970 grams per cubic centimeter, and preferably has a density in the range of 0.870 to 0.930 grams per cubic centimeter. They can also have a melt index in the range of 0.1 to 50 grams per 10 minutes. If the polyethylene is a homopolymer, its melt index is preferably in the range of 0.75 to 3 grams per 10 minutes. The melt index is determined according to ASTM D-1238, Condition E and is measured at 190 ° C. and 2160 grams.

  Polyethylene can be produced by low pressure or high pressure processes. Polyethylene can be produced by conventional techniques in gas phase processes or liquid phase processes (ie, solution or slurry processes). Low pressure processes are typically performed at pressures less than 1000 pounds per square inch ("psi"), while high pressure processes are typically performed at pressures greater than 15,000 psi.

  Typical catalyst systems for preparing these polyethylenes include magnesium / titanium based catalyst systems, vanadium based catalyst systems, chromium based catalyst systems, metallocene catalyst systems, and other transitions. Metal catalyst systems are mentioned. Many of these catalyst systems are often referred to as Ziegler-Natta catalyst systems or Phillips catalyst systems. Useful catalyst systems include catalysts that use chromium or molybdenum oxides supported on a silica-alumina support.

  Useful polyethylenes include low density ethylene homopolymer (HP-LDPE), linear low density polyethylene (LLDPE), very low density polyethylene (VLDPE), very low density polyethylene (ULDPE), medium density made by high pressure processes. Examples include polyethylene (MDPE), high density polyethylene (HDPE), and metallocene copolymers.

  The high pressure process is typically radical initiated polymerization and is carried out in a tubular reactor or stirred autoclave. For a tubular reactor, the pressure is in the range of 25,000 to 45,000 psi and the temperature is in the range of 200 to 350 ° C. For a stirred autoclave, the pressure is in the range of 10,000 to 30,000 psi and the temperature is in the range of 175 to 250 ° C.

  The VLDPE or ULDPE can be a copolymer of ethylene and one or more α-olefins having 3 to 12 carbon atoms, preferably 3 to 8 carbon atoms. The density of VLDPE or ULDPE can range from 0.870 to 0.915 grams per cubic centimeter. The melt index of VLDPE or ULDPE can range from 0.1 to 20 grams per 10 minutes and is preferably in the range of 0.3 to 5 grams per 10 minutes. The portion of the VLDPE or ULDPE derived from the comonomer (s) other than ethylene can range from 1 to 49% by weight, preferably in the range from 15 to 40% by weight, based on the weight of the copolymer. is there.

  A third comonomer can be included, for example, another α-olefin, or a diene such as ethylene norbornene, butadiene, 1,4-hexadiene, or dicyclopentadiene. The ethylene / propylene copolymer is commonly referred to as EPR and the ethylene / propylene / diene terpolymer is generally referred to as EPDM. The third comonomer can be present in an amount of 1 to 15 wt%, preferably in an amount of 1 to 10 wt%, based on the weight of the copolymer. The copolymer preferably comprises 2 or 3 comonomers including ethylene.

  LLDPE can include VLDPE, ULDPE, and MDPE, which are linear, but generally has a density in the range of 0.916 to 0.925 grams per cubic centimeter. This can be a copolymer of ethylene and one or more α-olefins having 3 to 12 carbon atoms, preferably 3 to 8 carbon atoms. Its melt index can be in the range of 1 to 20 grams per 10 minutes, preferably in the range of 3 to 8 grams per 10 minutes.

  Any polypropylene can be used in these compositions. Examples include homopolymers of propylene, copolymers of propylene and other olefins, and terpolymers of propylene, ethylene and dienes (eg, norbornadiene and decadiene). In addition, the polypropylene can be dispersed with or blended with other polymers such as EPR or EPDM. Suitable polypropylenes include TPE, TPO, and TPV. Examples of polypropylene are described in POLYPROPYLENE HANDBOOK: POLYMERIZATION, CHARACTERIZATION, PROPERIES, PROCESSING, APPLICATIONS 3-14, 113-176 (E. Moore, Jr., 1996).

  Suitable second polyolefins include polar polyolefins and amorphous first polyolefins. Examples of polar polyolefins are copolymers of ethylene and unsaturated esters such as vinyl esters (eg vinyl acetate or acrylic acid or methacrylic acid esters).

  Copolymers consisting of ethylene and unsaturated esters are well known and can be prepared by conventional high pressure techniques. The unsaturated ester can be an alkyl acrylate, an alkyl methacrylate, or a vinyl carboxylate. The alkyl group can have 1 to 8 carbon atoms, and preferably has 1 to 4 carbon atoms. The carboxylic acid group can have 2 to 8 carbon atoms, and preferably has 2 to 5 carbon atoms. Examples of acrylate and methacrylate esters are ethyl acrylate, methyl acrylate, methyl methacrylate, t-butyl acrylate, n-butyl acrylate, n-butyl methacrylate, and 2-ethylhexyl acrylate. Examples of vinyl carboxylates are vinyl acetate, vinyl propionate, and vinyl butanoate. Preferably, the unsaturated ester is present in an amount from about 1.0% to about 3.0% by weight.

  Suitable vinylalkoxysilanes include, for example, vinyltrimethoxysilane and vinyltriethoxysilane. Preferably, the vinylalkoxysilane is present in an amount from about 1.0% to about 2.0% by weight.

  For example, suitable organic peroxides include dialkyl peroxide, dicumyl peroxide, and Vulcup R. The organic peroxide is preferably from about 0.03% to about 5.0%, more preferably from about 0.05% to about 2.0%, even more preferably from about 0.05% by weight. It is present in an amount of about 1.0% by weight, most preferably from about 0.05% to about 0.08% by weight.

  The composition comprises (a) a phenolic antioxidant, (b) a thio antioxidant, (c) a phosphate antioxidant, and (d) a hydrazine metal deactivator. An inhibitor may further be included. Suitable phenolic antioxidants include methyl substituted phenols. Other phenols having substituents containing primary or secondary carbonyls are suitable antioxidants. A preferred phenolic antioxidant is isobutylidenebis (4,6-dimethylphenol). A preferred hydrazine-based metal deactivator is oxalyl bis (benzylidiene hydrazide). Preferably, the antioxidant is present in an amount from 0.05% to 10% by weight of the polymer composition.

  The composition may further comprise polyvinyl chloride, acrylic resin, polyamide, polyester, polyester urethane, shape memory polymer, carbon black, colorant, corrosion inhibitor, lubricant, anti-blocking agent, flame retardant, and processing aid. Good.

  In an alternative embodiment, the present invention is a wire or cable structure prepared by applying a polymer composition to the wire or cable.

  In another embodiment, the present invention provides a process for making a crosslinked article. This process allows crosslinking at ambient temperature and humidity conditions without the use of a sulfonic acid catalyst or without causing acid-catalyzed destruction of the hindered phenolic antioxidant.

  The invention is illustrated by the following non-limiting examples.

  Each of the compositions illustrated in Table 1 was prepared using 2.0 wt% vinyltrimethoxysilane and 0.08 wt% LUPEROX 101 organic peroxide. The polymer was conditioned at 40 ° C. for 2 hours.

  Each of the compositions illustrated in Table 3 uses 2.0 wt% vinyltrimethoxysilane, 0.08 wt% LUPEROX 101 organic peroxide, and 5.0 wt% DFDB-5482 catalyst masterbatch. Prepared. The polymer was conditioned at 40 ° C. for 2 hours.

Claims (6)

(A) a polymer matrix comprising a first polyolefin,
(B) a second polyolefin selected from the group consisting of polar polyolefins and amorphous polyolefins dispersed in a polymer matrix;
(C) a moisture-crosslinkable composition comprising vinylalkoxysilane, and (d) an organic peroxide. (A) a copolymer of the first polyolefin and a second polyolefin selected from the group consisting of polar polyolefins and amorphous polyolefins;
A moisture-crosslinkable composition comprising (b) vinylalkoxysilane, and (c) an organic peroxide.   The moisture-crosslinkable composition according to claim 1 or 2, wherein the organic peroxide is present in an amount of 0.05 wt% to 0.08 wt%. A process for moisture crosslinking a polyolefin composition comprising:
(A) selecting a first polyolefin;
(B) selecting a second polyolefin;
(C) dispersing the second polyolefin in the first polyolefin to form a polyolefin composition;
(D) absorbing the silane into the second polyolefin;
(E) absorbing the organic peroxide in the second polyolefin;
(F) mixing a moisture crosslinking catalyst;
(G) a process consisting essentially of crosslinking the polyolefin composition. A process for moisture crosslinking a polyolefin composition comprising:
(A) selecting a copolymerized polyolefin having the copolymer as a first polyolefin and a second polyolefin;
(B) absorbing the silane into the copolymerized polyolefin;
(C) absorbing the organic peroxide into the copolymerized polyolefin;
(D) mixing a moisture crosslinking catalyst;
(E) a process consisting essentially of crosslinking the polyolefin composition.   The process according to claim 4 or 5, wherein the crosslinking step is carried out at ambient temperature and humidity.

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